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61.
Qualitative and quantitative analyses of phenolic compounds are of interest for both medicinal and food plants. In the present work, the phenolic fraction from Yucca schidigera, a plant bearing the GRAS (Generally Recognized as Safe) label approved by the US Food and Drug Administration, was studied. Crude extracts of Y. schidigera bark were investigated by liquid chromatography/UV spectrophotometry with diode-array detection, liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) and liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS), in order to develop and optimize simple and rapid techniques to determine both stilbenes and yuccaols for the purposes of quality control of collected material. With optimal LC and MS conditions, stilbenes and yuccaols were quantified with all the proposed methods and the results were compared. Sensitivity was evaluated and the results indicated that MS/MS detection in the multiple reaction monitoring mode is easily applicable to this plant and allows the rapid and direct identification and quantification of these peculiar compounds in crude plant extracts. 相似文献
62.
Michal W. Wieczorek Wieslaw Majzner Magdalena Sikora Jzef Kula 《Heteroatom Chemistry》1995,6(6):525-531
During the transformation process of limonene to tetrahydrofuran derivatives, the title compounds (±)-( 4 ) have been obtained as crystalline products and subjected to X-ray analysis. The crystals of trans-( 4 ) are orthorhombic, space group P212121, with the lattice constants a = 7.0445(5) Å, b = 10.0908(4) Å, c = 14.0309(6) Å; the absolute configuration at atoms C1, C2, and C4 is Rc1, Sc2, and Rc4, respectively. The isomeric form cis-( 4 ) crystallizes in the monoclinic system, space group P21, with the following unit-cell parameters: a = 10.8275(4) Å, b = 8.6994(5) Å, c = 16.4722(6) Å, β = 106.515(3)°. The asymmetric part of the unit cell of cis-( 4 ) contains three independent molecules. Each of these three molecules has the identical absolute configuration at all centers of chirality: Sc1, Sc2, and Rc4. © John Wiley & Sons, Inc. 相似文献
63.
Jaroslaw Chojnacki Barbara Becker Antoni Konitz Wieslaw Wojnowski 《无机化学与普通化学杂志》2000,626(10):2173-2177
Compounds of general formula Au{SSi(OR)3}(PPh3), R = Pri ( 1 ), Bus ( 2 ) or But ( 3 ), have been obtained by reaction of AuCl(PPh3) with triethylammonium salts of respective silanethiols, (RO)3SiSH. Molecular and crystal structures of 1 , 2 , and 3 have been determined by the single crystal X‐ray structural analysis. Compounds 1 and 2 are the first structurally characterized metal derivatives of hydrolytically unstable trialkoxysilanethiols (PriO)3SiSH and (BusO)3SiSH. 相似文献
64.
We study experimentally the Bloch-wave instabilities in optically induced photonic lattices. We reveal two different instability scenarios associated with either the transverse modulational instability of a single Bloch wave or the nonlinear interband coupling between different Bloch waves. We show that the transverse instability is greatly enhanced in the induced lattice in comparison with homogeneous media. 相似文献
65.
Gauthier PA Berry A Woszczyk W 《The Journal of the Acoustical Society of America》2005,117(2):662-678
This paper describes the simulations and results obtained when applying optimal control to progressive sound-field reproduction (mainly for audio applications) over an area using multiple monopole loudspeakers. The model simulates a reproduction system that operates either in free field or in a closed space approaching a typical listening room, and is based on optimal control in the frequency domain. This rather simple approach is chosen for the purpose of physical investigation, especially in terms of sensing microphones and reproduction loudspeakers configurations. Other issues of interest concern the comparison with wave-field synthesis and the control mechanisms. The results suggest that in-room reproduction of sound field using active control can be achieved with a residual normalized squared error significantly lower than open-loop wave-field synthesis in the same situation. Active reproduction techniques have the advantage of automatically compensating for the room's natural dynamics. For the considered cases, the simulations show that optimal control results are not sensitive (in terms of reproduction error) to wall absorption in the reproduction room. A special surrounding configuration of sensors is introduced for a sensor-free listening area in free field. 相似文献
66.
Damian Pociecha Jadwiga Szydlowska Julita Gasowska Dorota Kardas J zef Mieczkowski Wieslaw Tlaczala 《Liquid crystals》2002,29(5):663-667
Two homologous series of mesogenic materials with molecules containing an amide moiety, cyclic or symmetrically branched, as the terminal group have been synthesized. Materials of both series form lamellar liquid crystal phases. It was observed that elongation of the amide chains in 'fork-like' compounds destabilizes the mesophases, while 'cyclic' materials, even with quite large terminal amide rings, exhibit enantiotropic liquid crystalline phases. 相似文献
67.
68.
Effects of the method of identification of the diffusion coefficient on accuracy of modeling bound water transfer in wood 总被引:2,自引:0,他引:2
An alternative approach to determining the bound water diffusion coefficient is proposed. It comprises a method for solving
the inverse diffusion problem, an improved algorithm for the bound-constrained optimization as well as an alternative submodel
for the diffusion coefficient’s dependency on the bound water content. Identification of the diffusion coefficient for Scots
pine wood (Pinus sylvestris L.) using the proposed inverse approach is presented. The accuracy of predicting the diffusion process with the use of the
coefficient values determined by traditional sorption methods as well as by the inverse modeling approach is quantified. The
similarity approach is used and the local and global relative errors are calculated. The results show that the inverse method
provides valuable data on the bound water diffusion coefficient as well as on the boundary condition. The results of the identification
can significantly improve the accuracy of mass transfer modeling as studied for drying processes in wood. 相似文献
69.
An observation of negative refraction in the naturally obtained composition of graphene and barium ferrite is reported. The capacitance and inductance measurements revealed the electric and magnetic resonances accompanied with the negative values of permittivity and permeability in the overlapped frequency range. According to the “left‐handed” media approach such a material is characterized by negative refraction. The derived values of the real part of refractive index are negative at the frequencies above 500 MHz.
70.
Abstract The liquid crystalline properties of 1-(alkylamino)-3-[(4″-hexyl-trans-cyclohexyl-4′-phenyl]-prop-1-en-3-one-s, from methyl to octadecyl, and their copper (II) complexes have been examined by optical, DSC, X-ray and EPR methods. The compounds are enantiotropic nematogens except those having the shortest and the longest terminal chains. Short chains promote the SA phase in both ligands and complexes, whereas long chains promote SC and crystal H phases for the ligands or SA and SC phases for the complexes. A partly bilayer smectic Ad phase is observed from ligands terminated with short non-polar substituents. Direct isotropisation from the crystal H phase for some of the compounds, as well as other phase transitions have been studied. The molecular shape of the complexes and the organization of their mesomorphic phases are discussed, based on the refractive indices and X-ray data. 相似文献