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131.
132.
Kostadinova E Nikolova D Alipieva K Stefova M Stefkov G Evstatieva L Matevski V Bankova V 《Natural product research》2007,21(9):819-823
The essential oils of two species of Sideritis growing spontaneously in Bulgaria and Macedonia are reported, Sideritis scardica and Sideritis raeseri. The oils of S. scardica from different locations differed significantly: in the Macedonian sample alpha-cadinol (20%) predominated, while in the oil of Bulgarian samples the main components were diterpenic compounds and octadecenol (over 20%). This is the first report of ditrpenoids in essential oil of S. scardica. The oil of S. raeseri demonstrated a distinct chemical profile with its high concentration of sesquiterpenes, main components being germacrone (25%) and elemol acetate (15.9%). The observed qualitative variability of the oil composition of S. scardica of different geographic origin could be a result of different ecologic conditions but might also reflect the well-known tendency of some Sideritis species to hybridize. 相似文献
133.
Trendafilova A Todorova M Nikolova M Gavrilova A Vitkova A 《Natural product communications》2011,6(12):1851-1854
Antioxidant capacity of the methanolic extract of Alchemilla mollis was measured by its ability to scavenge the DPPH radical. The EtOAc fraction obtained after partition of the total extract was found to be the most active radical scavenger (IC50 9.8 +/- 1.8 microg/mL) and was subjected to fractionation by Sephadex LH-20 CC. Further purification by RP-18 CC led to the isolation of eight flavonoid glycosides: cis- and trans-tiliroside (1 and 2), rhodiolgin (3), hyperoside (4), isoquercitrin (5), miquelianin (6), sinocrassoside D2 (7), and gossypetin-3-O-beta-D-galactopyranosyl-7-O-alpha-L-rhamnopyranoside (8). It was found that 8 is a new compound and its antioxidant activity is also reported. Identification of the isolated compounds was carried out by spectroscopic and spectrometric analysis (1D and 2D NMR, UV and MS). 相似文献
134.
Barbara Gambin Jordanka Ivanova Varbinka Valeva Gergana Nikolova 《Acta Mechanica Sinica》2011,27(1):80-89
The behavior of a precracked bi-material structure interface under given static and dynamic axial loading is an interest object in the present paper.Firstly,it is shown that the shear-lag model is a proper tool to analyze a delamination process in a precracked bi-material structure undergoing static loading.Secondly,the"shear-lag model"is applied to the structure under dynamic loading.To solve the problem for an interface delamination of the structure and to determine the debond length along the interface,our own 2D boundary element method(BEM)code is proposed in the case of static loading,and the shear-lag model together with the Laplace transforms and half-analytical calculations are used in the case of dynamic loading.The interface layer is assumed as a very thin plate compared with the other two.The parametric(geometric and elastic)analysis of the debond length and interface shear stress is done. The results from the 2D BEM code proved the validity of analytical solutions to the shear-lag model.In the dynamic case,the influence of loading characteristics,i.e.,frequencies and amplitude fluctuations on the shear stress and the value of debond length for an interval of time,is discussed. The analysis of the obtained results is illustrated by an example of the modern ceramic-metal composite,namely cermet, and depicted in figures. 相似文献
135.
Anestis Antoniadis Irène Gijbels Mila Nikolova 《Annals of the Institute of Statistical Mathematics》2011,63(3):585-615
One of the popular method for fitting a regression function is regularization: minimizing an objective function which enforces
a roughness penalty in addition to coherence with the data. This is the case when formulating penalized likelihood regression
for exponential families. Most of the smoothing methods employ quadratic penalties, leading to linear estimates, and are in
general incapable of recovering discontinuities or other important attributes in the regression function. In contrast, non-linear
estimates are generally more accurate. In this paper, we focus on non-parametric penalized likelihood regression methods using
splines and a variety of non-quadratic penalties, pointing out common basic principles. We present an asymptotic analysis of convergence rates that justifies the
approach. We report on a simulation study including comparisons between our method and some existing ones. We illustrate our
approach with an application to Poisson non-parametric regression modeling of frequency counts of reported acquired immune
deficiency syndrome (AIDS) cases in the UK. 相似文献
136.
137.
A new approach is proposed for the study of short-range molecular interactions between first neighboring molecules in amphiphile bilayers by means of experimentally determined dependencies of the bilayer mean lifetime on the surfactant concentration and of the critical concentration for bilayer formation on the temperature. Short-range molecular interactions are demonstrated by the parameters binding energy Q of an amphiphile molecule in the bilayer and specific line energy γ of the nucleus hole. These parameters are calculated from the experimental dependencies by using the hole-nucleation theory [D. Kashchiev and D. Exerowa, J. Colloid Interface Sci., 77, 501 (1980)] describing the stability of amphiphile bilayers. It is shown the decisive role of the short-range molecular interactions for the bilayer stability and the occurrence of first-order phase transition in phospholipid foam bilayers. The values of Q and γ are calculated for various amphiphile bilayers: anionic and nonionic surfactants, phospholipids and their natural mixtures. 相似文献
138.
Rositca D. Nikolova Sonya Zareva Anka G. Bojilova Tsonko Kolev Bojidarka Koleva 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2998-3012
Correlation between the structure and IR-spectroscopic properties of two halogen and one amino substituted esters of coumarin-3-phosphonic acid has been studied by means of linear-polarized IR-spectroscopy of oriented colloid suspensions in nematic host. The influence of the ester group on the peak positions of the IR-characteristic bands of these derivatives and in particular, on phosphorus group is investigated by a comparison with the data for corresponding coumarin-3-phosphonic acids. Theoretical quantum chemical DFT calculations (B3LYP/6-311++G??) are carried out, thus supporting the experimental assignment of the IR-bands and predicting the electronic structure of all of the compounds studied. 相似文献
139.
Rositca D. Nikolova 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1626-1634
Abstract (2-Oxo-2H-chromen-3-yl)phosphonic acid monoethyl ester trihydrate (1) was synthesized, isolated, and spectroscopically as well as structurally characterized by means of single crystal X-ray diffraction; conventional and linear-polarized IR spectroscopy; electronic (UV-VIS-NIR) spectroscopy; 1H, 13C, and 31P NMR. Quantum chemical DFT calculations have been performed in order to obtain information on the electronic structure and vibrational properties of 1, thus supporting the experimental data. The correlation between the structure and spectroscopic characteristics is discussed. GRAPHICAL ABSTRACT 相似文献
140.
A newly found reaction for the synthesis of 3,4-disubstituted 1-hydroxy-pyrrolidine-2,5-diones from 3-substituted coumarins and nitromethane has been elaborated. The reaction involved a simple and convenient experimental procedure. The applicability of the rearrangement reaction is determined. 相似文献