Pyrrolizidine alkaloids from Solenanthus lanatus DC. with acetylcholinesterase inhibitory activity

The whole plant ethanolic extract of Solenanthus lanatus was used for the isolation of acetylcholinesterase inhibitors. A new pyrrolizidine alkaloid, 7-O-angeloylechinatine N-oxide, 1, was isolated together with three known compounds of the same class (3′-O-acetylheliosupine N-oxide, 2, heliosupine N-oxide, 3, and heliosupine, 4), by bioassay-guided approach. Their structures were elucidated by spectroscopic methods. All the isolated compounds showed inhibition activity against the AChE, with IC₅₀ 0.53–0.60 mM.     

Effect of relevant umklapp process on the two-leg Hubbard ladder with a half-filled band under pressure

By means of perturbative renormalization approach we study the effect of relevant umklapp process on dimensional crossover caused by interladder one particle hopping in weakly coupled two-leg Hubbard ladders with a half filled-band. We found that a crossover takes place at a finite value which increases as the amplitude of umklapp process increases. For the system undergoes a phase transition to the spin density wave phase (SDW) via the two particle hopping process, while for the system undergoes a crossover to the two dimensional Fermi liquid phase via one particle hopping process. Received 25 December 1998     

Formation of luminescent (NH4)2SiF6 phase from vapour etching-based porous silicon

In this paper we describe the formation of a luminescent (NH₄)₂SiF₆ via porous silicon (PS) obtained from HNO₃/HF vapour etching (VE) silicon (Si) substrates. It was found that at specific conditions, PS transforms in a luminescent thick white powder (WP) layer. Scanning electron microscopy (SEM) revealed that the WP has a coral-like structure. It was also found that PS persists as an intermediate layer between the Si substrate and the WP, and seems to be the seed that transforms into the WP. SEM microanalysis show that the WP is essentially composed of silicon (Si), nitrogen (N) and fluorine (F). Fourier transform infrared (FTIR) spectroscopy investigations show that this WP contains SiF₆²⁻ and NH₄⁺ ions and N---H chemical bonds. X-ray diffraction (XRD) patterns of the WP confirm that a (NH₄)₂SiF₆ cubic phase is concerned. SEM microanalyses show an excess of Si in the WP matrix. FTIR spectroscopy and XRD analysis reveal the presence of crystalline Si particles and SiO_x, both originating from the excess of Si. The (NH₄)₂SiF₆ WP phase emits an intense photoluminescence (PL) band, shifted towards higher energies as compared to the starting PS layer. The possible origin and mechanism of the luminescence emission was discussed taking into account the ability of small SiO_x-surrounded Si particles to emit PL at rather high energy. The wide range variation of the thickness of the (NH₄)₂SiF₆ WP may be easily used for the grooving of Si wafers.     

Contribution of the added masses in the dynamic modelling of flexible airships

This paper presents an efficient modelling of autonomous flexible airships. These flying objects lighter than air (L.T.A.) are assumed to undergo large rigid-body motion and small elastic deformation. The formalism used is based on the Euler–Lagrange approach. The airship considered in this study is represented by a flexible ellipsoid of revolution. The coupling between the added masses issued from the overall body motion and those issued from the elasticity was determined by means of the velocity potential flow theory. We develop a fully analytical methodology with some assumptions. This feature distinguishes the current work from earlier treatments of the coupling, it allows one to minimise the number of degrees of freedom of the dynamical model, and renders the model suitable for use in the algorithms of stabilisation and trajectory generation. Numerical simulations are presented at the end of this paper. They underline the interest of the developed theoretical results.     

Excitonic states of weakly one-dimensional quantum wires

Il Nuovo Cimento D - We report on calculations of excitonic properties of weakly one-dimensional quantum wires where the exciton centre of mass is quantized by the harmonic potentials of electron...     

Phytochemical profiles,antioxidant and anti-acetylcholinesterasic activities of the leaf extracts of Rhamnus lycioides subsp. oleoides (L.) Jahand. & Maire in different solvents

In this work, the extracts obtained with different solvents from the leaves of Rhamnus lycioides subsp. oleoides (L.) Jahand. & Maire were studied for their phytochemical profile and then for their antioxidant and acetylcholinesterase inhibitory activities. The phytochemical profiles of the extracts in n-hexane, dichloromethane, ethyl acetate, methanol, anthraquinone rich and water, showed the presence of different compounds belonging to several classes of natural products such as flavonoids, anthraquinones, saccharides and fatty acids. For what concerns the biological tests, the ethyl acetate, methanol and anthraquinone rich extracts showed the highest activities in both assays due to the high amount of compounds possessing those properties such as flavonoids and anthraquinones. By consequence, these specific extracts of the species may be considered to be potential sources of natural antioxidant and anti-acetylcholinesterasic compounds.     

Clique inference process for solving Max-CSP

Few works on problems CSP, Max-CSP and weighted CSP was carried out in the field of Combinatorial Optimization, whereas this field contains many algorithmic tools which can be used for the resolution of these problems.In this paper, we introduce the binary clique concept: clique which expresses incompatibilities between values of two CSP variables. We propose a linear formulation for any binary clique and we present several ways to exploit it in order to compute lower bounds or to solve Max-CSP. We also show that the binary clique concept can be exploited in the weighted CSP framework.The obtained theoretical and experimental results are very interesting and they open new prospects to exploit the Combinatorial Optimization algorithmic tools for the resolution of CSP, Max-CSP and weighted CSP.     

Morphological changes in porous silicon nanostructures: non-conventional photoluminescence shifts and correlation with optical absorption

In this paper, we show that the photoluminescence (PL) shifts of p-type porous silicon (PS) are mainly attributed to some morphological changes related to anodisation conditions. We discuss how differences in the stirring and nature of the electrolytic solution can lead to morphological changes of the PS layers. It has been found that when PS is formed in pure aqueous HF solution, it can exhibit a non-conventional and reproducible “porosity – PL peak relationship”. By correlating the PL spectral behaviour and PS morphology throughout a quantum-confinement model, we explain both conventional and non-conventional PL shifts. Correlation of PL and optical absorption (OA) shows that the PL peak energy and the optical absorption edge of PS exhibit the same trend with size effect. The spectral behaviour of OA with regard to that of PL is well analysed within the quantum-confinement model throughout the sizes and shapes of the nanocrystallites forming PS. The value of the effective band gap energy determined from the calculated lowest PL energy almost corresponds to that estimated from the optical absorption coefficient. These results suggest that the lowest radiative transition between the valence band and the conduction band corresponds to the largest luminescent wires, and that the radiative recombination process leading to the PL emission occurs in the c-Si crystallite core.