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31.
Fernanda Cosme Alice Vilela Luís Moreira Carla Moura Jos A. P. Enríquez Luís Filipe-Ribeiro Fernando M. Nunes 《Molecules (Basel, Switzerland)》2020,25(24)
‘Mencía’/‘Jaen’ it’s an important red grape variety, exclusive of the Iberian Peninsula, used in wine production namely in Bierzo D.O. and Dão D.O., respectively. This work evaluates the effect of the two different “terroirs” on the phenolic composition and chromatic characteristics of ‘Mencía’/‘Jaen’ monovarietal wines produced at an industrial scale in the same vintage. Using Principal Component Analysis (PCA), Partial Least Squares-Discrimination Analysis (PLS-DA), and Orthogonal PLS-DA (OPLS-DA) it was found that peonidin-3-coumaroylglucoside, petunidin-3-glucoside, malvidin-3-coumaroylglucoside, peonidin-3-glucoside, malvidin-3-acetylglucoside, malvidin-3-glucoside, and ferulic acid were the phenolic compounds with the highest differences between the two regions. PLS regression allowed to correlate the differences in lightness (L*) and redness (a*) of wines from ‘Jaen’ and ‘Mencía’ to differences in colored anthocyanins, polymeric pigments, total pigments, total anthocyanins, cyanidin-3-acetylglucoside, delphinidin-3-acetylglucoside, delphinidin-3-glucoside, peonidin-3-coumaroylglucoside, petunidin-3-glucoside and malvidin-3-glucoside in wines, and the colorless ferulic, caffeic, and coutaric acids, and ethyl caffeate. The wines a* values were more affected by colored anthocyanins, ferulic acid, total anthocyanins, delphinidin-3-acetylglucoside, delphinidin-3-glucoside and petunidin-3-acetylglucoside, and catechin. The positive influence of ferulic acid in the a* values and ferulic, caffeic, coutaric acids, and ethyl caffeate on the L* values can be due to the co-pigmentation phenomena. The higher dryness and lower temperatures during the September nights in this vintage might explain the differences observed in the anthocyanin content and chromatic characteristics of the wines. 相似文献
32.
Ruben Elvas-Leito Filomena Martins Leonor Borbinha Catarina Marranita Angela Martins Nelson Nunes 《Molecules (Basel, Switzerland)》2020,25(23)
Attempts to optimize heterogeneous catalysis often lack quantitative comparative analysis. The use of kinetic modelling leads to rate (k) and relative sorption equilibrium constants (K), which can be further rationalized using Quantitative Structure-Property Relationships (QSPR) based on Multiple Linear Regressions (MLR). Friedel-Crafts acylation using commercial and hierarchical BEA zeolites as heterogeneous catalysts, acetic anhydride as the acylating agent, and a set of seven substrates with different sizes and chemical functionalities were herein studied. Catalytic results were correlated with the physicochemical properties of substrates and catalysts. From this analysis, a robust set of equations was obtained allowing inferences about the dominant factors governing the processes. Not entirely surprising, the rate and sorption equilibrium constants were found to be explained in part by common factors but of opposite signs: higher and stronger adsorption forces increase reaction rates, but they also make the zeolite active sites less accessible to new reactant molecules. The most relevant parameters are related to the substrates’ molecular size, which can be associated with different reaction steps, namely accessibility to micropores, diffusion capacity, and polarizability of molecules. The relatively large set of substrates used here reinforces previous findings and brings further insights into the factors that hamper/speed up Friedel-Crafts reactions in heterogeneous media. 相似文献
33.
34.
Glutamic acid (H2glu) and its lithium, sodium
and ammonium monosalts were submitted to thermal analysis using thermogravimetry
(TG) and differential thermal analysis (DTA). The main goal of these studies
was to compare the relative thermal stability and to evaluate the effect of
the counter ion in the thermal decomposition pathways. Salts were obtained
by direct neutralization of the purified acid with LiOH, NaOH or NH4OH
and were characterized by elemental analysis (C, H and N) and IR spectroscopy.
Decomposition occurred after conversion to the pyroglutamic acid or the respective
pyroglutamates and ammonium salt loosing NH3 being
converted to H2glu before decomposition. 相似文献
35.
36.
A. F.R. Rodriguez J. G. Santos L. B. Silveira A. C. Oliveira P. C. Morais O. A.C. Nunes 《The European physical journal. Special topics》2008,153(1):543-546
Photoacoustic spectroscopy (PAS) was used to investigate
samples produced from Baru (Dipteryx alata Vog.), a typical fruit from the Brazilian
Cerrado, which is considered as a good source of nutrients. The
photoacoustic (PA) spectra of samples prepared from Baru seeds present three
different absorption bands in the wavelength range 0.3–1.0 μm, named
Band-C, Band-S, and Band-L. We found that PAS can be useful for monitoring
the strong absorption of visible light by Baru's seeds constituents mainly
in the shorter wavelength measured range. This study is important from both
agricultural and commercial point of view once it introduces PAS as a
potential characterization technique allowing better control of fruit and
seed selection, storage and transportation. 相似文献
37.
Carlos A. FlorentinoJosé M. Mourão João P. Nunes 《Journal of Functional Analysis》2002,192(2):410-424
We extend the coherent state transform (CST) of Hall to the context of abelian varieties by considering them as quotients of the complexification of the abelian group K=U(1)g. We show that this transform, applied to appropriate distributions on K, gives all classical theta functions, and that, by defining on this space of theta functions an inner product related to the K-averaged heat kernel, the unitarity of the CST transform is still preserved. 相似文献
38.
O.A.C. Nunes 《Solid State Communications》1983,45(6):521-525
The free-carrier multiphoton absorption of laser radiation in magnetic semiconductors in the presence of quantizing magnetic fields is discussed. It is found that for the laser frequency near the cyclotron frequency of the free carrier the magnon population may become unstable. 相似文献
39.
We present an investigation of the excited-state absorption and laser emission of a 1.0-at. %-Nd3+-doped YVO4 single-crystal fiber grown by the low-cost and versatile laser-heated pedestal growth technique. Efficient laser emission at 1064 nm was achieved when the fiber was pumped, in an end-pump cavity, by a Ti:sapphire laser at 808 nm. A continuous-wave threshold of 10 mW was observed with an efficiency of 42% with respect to the absorbed pump power and the maximum output power of 200 mW. These results are excellent when compared with those of a commercial bulk crystal adapted to the same cavity (48% efficiency, 250-mW maximum output power). Thus the fibers are characterized as strong candidates for the construction of compact lasers that can also be pumped by low-cost diode lasers. 相似文献
40.
Ivanov PC Nunes Amaral LA Goldberger AL Havlin S Rosenblum MG Stanley HE Struzik ZR 《Chaos (Woodbury, N.Y.)》2001,11(3):641-652
We explore the degree to which concepts developed in statistical physics can be usefully applied to physiological signals. We illustrate the problems related to physiologic signal analysis with representative examples of human heartbeat dynamics under healthy and pathologic conditions. We first review recent progress based on two analysis methods, power spectrum and detrended fluctuation analysis, used to quantify long-range power-law correlations in noisy heartbeat fluctuations. The finding of power-law correlations indicates presence of scale-invariant, fractal structures in the human heartbeat. These fractal structures are represented by self-affine cascades of beat-to-beat fluctuations revealed by wavelet decomposition at different time scales. We then describe very recent work that quantifies multifractal features in these cascades, and the discovery that the multifractal structure of healthy dynamics is lost with congestive heart failure. The analytic tools we discuss may be used on a wide range of physiologic signals. (c) 2001 American Institute of Physics. 相似文献