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101.
Jay D. Mancini Vassilios Fessatidis Robert K. Murawski Samuel P. Bowen 《Brazilian Journal of Physics》2014,44(4):305-307
Anumber of years ago, a calculational scheme was introduced by Stubbins [Phys. Rev. A48, 220 (1993)] to compute the energies of both the Hulthén and Yukawa potentials. The method introduces a particular ansatz for solving the Schrödinger equation with screened Coulomb type potentials. In this work, we wish to review the method of Stubbins and to show that it is, in fact, equivalent and a subset of a more systematic (and hence more useful) variational scheme [Zhou et al. Phys. Rev. A51, 3337 (1995)]. This variational approach involves the construction of a basis by taking derivatives of the variational parameters of the system. The eigenvalues of the Hamiltonian matrix are then minimized with respect to these parameters yielding a “best guess” upper bound on the energies. 相似文献
102.
The electrochemical characteristics of a La0.8Sr0.2Co0.2Fe0.8O3 − δ cathode electrode interfaced to the CGO layer of a double layer CGO/YSZ electrolyte were studied using cyclic voltammetry, at temperatures of 600 to 850 °C and under oxygen partial pressures ranging from 0.07 to 21 kPa. The aim was to identify the electrochemical processes taking place under cathodic polarization on the basis of differences in the features of the cyclic voltammograms with changing conditions. Depending on temperature, sweep rate and oxygen partial pressure, current peaks appeared both in the forward and backward scans. Furthermore, reversed hysteresis was observed, i.e. higher currents in the backward scan than in the forward scan, with increasing oxygen partial pressure and decreasing temperature. The observed behavior was related to the electrochemical redox of B-sites and concomitant stoichiometry change as well as to the competing reaction of electrochemical oxygen redox, taking also into account the competitive action of chemical reactions occurring in the presence of gaseous oxygen. 相似文献
103.
Petersen RK Christensen KB Assimopoulou AN Fretté X Papageorgiou VP Kristiansen K Kouskoumvekaki I 《Journal of computer-aided molecular design》2011,25(2):107-116
In a search for more effective and safe anti-diabetic compounds, we developed a pharmacophore model based on partial agonists
of PPARγ. The model was used for the virtual screening of the Chinese Natural Product Database (CNPD), a library of plant-derived
natural products primarily used in folk medicine. From the resulting hits, we selected methyl oleanonate, a compound found,
among others, in Pistacia lentiscus var. Chia oleoresin (Chios mastic gum). The acid of methyl oleanonate, oleanonic acid, was identified as a PPARγ agonist
through bioassay-guided chromatographic fractionations of Chios mastic gum fractions, whereas some other sub-fractions exhibited
also biological activity towards PPARγ. The results from the present work are two-fold: on the one hand we demonstrate that
the pharmacophore model we developed is able to select novel ligand scaffolds that act as PPARγ agonists; while at the same
time it manifests that natural products are highly relevant for use in virtual screening-based drug discovery. 相似文献
104.
105.
Quantitative determination of alkannins and shikonins in endemic Mediterranean Alkanna species 下载免费PDF全文
Jasmin Tappeiner Alexandra Vasiliou Markus Ganzera Dimitrios Fessas Hermann Stuppner Vassilios P. Papageorgiou Andreana N. Assimopoulou 《Biomedical chromatography : BMC》2014,28(7):923-933
The optical antipodes alkannin/shikonin (A/S) and their esters are potent pharmaceutical substances found in the roots of 150 Boraginaceous species. This study estimated and compared total and free A/S content and A/S enantiomeric ratio in roots of 11 Alkanna species (A. corcyrensis, A. tinctoria, A. pindicola, A. orientalis, A. methanaea, A. calliensis, A. graeca, A. primuliflora, A. stribrnyi, A. sieberi and A. noneiformis) growing wild in various Greek regions, to compare with cultivated species. It also re‐characterized the chirality of A/S commercial samples, since most of them were misnamed by the providers. Several Alkanna species were collected (groups 1 and 3) and botanically identified, whereas some Alkanna species were cultivated from collected seeds (group 2). Free A/S and derivatives were extracted from the dried roots of Alkanna species and analyzed by high performance liquid chromatography‐diode array detection (HPLC‐DAD). For total A/S content the hexane extracts of Alkanna roots were hydrolyzed and analyzed by HPLC‐DAD. Chirality determination and A/S enantiomeric ratio estimation was performed for several commercial samples by polarimetry,chiral LC‐DAD and circular dichroism studies. Quantitative analysis revealed that A/S content varied from one region to another even within the same species. Most of the cultivated samples contained greater amounts of free and total A/S compared with the wild ones, wheras no difference was observed in A/S enantiomeric ratio. All the Alkanna samples tested contain mainly alkannin derivatives. Some of the examined Alkanna species of the Greek flora that are endemic to the Mediterranean area could serve as alternative sources for medicinally valuable A/S derivatives. Most of the commercial A/S samples tested were misnamed in terms of chirality and re‐characterized. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
106.
107.
In this work solutions of the spectral Navier equation that satisfy the Herglotz boundedness condition in two-dimensional
linear elasticity are presented. Navier eigenvectors in polar coordinates are introduced and it is established that they form
a linearly independent and complete set in the L
2-sense on every smooth curve. It is also proved that the classical solutions of the spectral Navier equation are expressed
via Navier eigenvectors, and this expansion converges uniformly over compact subsets of R
2. Two far-field patterns, the longitudinal and the transverse one corresponding to the displacement field are introduced,
and the Herglotz norm is expressed as the sum of the L
2-norms of these patterns over the unit circle. It is also established that the space of elastic Herglotz functions is dense
in the space of the classical solutions of the spectral Navier equation. Finally, connection to inverse elasticity scattering
is established and reconstructions of rigid bodies are presented.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
108.
Fotios Petropoulos Spyros Makridakis Vassilios Assimakopoulos Konstantinos Nikolopoulos 《European Journal of Operational Research》2014
Forecasting as a scientific discipline has progressed a lot in the last 40 years, with Nobel prizes being awarded for seminal work in the field, most notably to Engle, Granger and Kahneman. Despite these advances, even today we are unable to answer a very simple question, the one that is always the first tabled during discussions with practitioners: “what is the best method for my data?”. In essence, as there are horses for courses, there must also be forecasting methods that are more tailored to some types of data, and, therefore, enable practitioners to make informed method selection when facing new data. The current study attempts to shed light on this direction via identifying the main determinants of forecasting accuracy, through simulations and empirical investigations involving 14 popular forecasting methods (and combinations of them), seven time series features (seasonality, trend, cycle, randomness, number of observations, inter-demand interval and coefficient of variation) and one strategic decision (the forecasting horizon). Our main findings dictate that forecasting accuracy is influenced as follows: (a) for fast-moving data, cycle and randomness have the biggest (negative) effect and the longer the forecasting horizon, the more accuracy decreases; (b) for intermittent data, inter-demand interval has bigger (negative) impact than the coefficient of variation; and (c) for all types of data, increasing the length of a series has a small positive effect. 相似文献
109.
Molecular dynamics simulation are used to examine the effect of a uniform perpendicular magnetic field on a two-dimensional interacting electron system. In this simulation we include the effect of the magnetic field classically through the Lorentz force. Both the Coulomb and the magnetic forces are included directly in the electron dynamics to study their combined effect on the dynamical properties of the 2D system. Results are presented for the velocity autocorrelation function and the diffusion constants in the presence and absence of an external magnetic field. Our simulation results clearly show that the external magnetic field has an effect on the dynamical properties of the system. 相似文献
110.