Hartley’s oscillator: The simplest chaotic two-component circuit

This paper shows an experimental evidence of chaos in one of the simplest imaginable autonomous implicit Hartley’s oscillator made simply of a junction field effect transistor (JFET) and a tapped coil. The experimental setup is implemented. The variations of amplitude of the oscillations through the control element are obtained showing the domain of existence of chaos. Phase portraits of the PSpice simulation, of the numerical integration and of the experiment are displayed, confirming a good agreement between theory and praxis.     

Cytotoxic effect of some pentacyclic triterpenes and hemisynthetic derivatives of stigmasterol

Two different oxidation reactions (PCC and KMnO₄) of stigmasterol gave three products, stigmasta-4,22-dien-3-one (1a), stigmasta-4,22-diene-3,6-dione (1b), and 3-O-acetyl-5β,6β-epoxystigmast-22-ene-3-ol (1c). The cytotoxic activities of hemisynthetic compounds, stigmasterol, and four pentacyclic triterpens 2–5 previously isolated from cultivated and wild Triumfetta cordifolia and identified were investigated against human fibrosarcoma cell line (HT1080). Most of the drugs showed moderate cytotoxic activity. It was also notice that the triterpene skeleton had a range of number of OH functions in which activity was observed. Spectroscopic analyses (¹H and ¹³ C NMR) and mass were used to elucidate the structure of hemisynthetic compounds.     

Moduli of Quaternionic Superminimal Immersions of 2-Spheres into Quaternionic Projective Spaces

The aim of this paper is to describe the moduli spaces of degree d quaternionic superminimal maps from 2-spheres to quaternionic projective spaces HPn. We show that such moduli spaces have the structure of projectivized fibre products and are connected quasi-projective varieties of dimension 2nd + 2n + 2. This generalizes known results for spaces of harmonic 2-spheres in S⁴.     

Long-chain alkanoic acid esters of lupeol from Dorstenia harmsiana Engl. (Moraceae)

In addition to lupeol (1a), three long-chain alkanoic acid esters of lupeol, in which two were new, were isolated from the hexane and ethyl acetate twigs extract of Dorstenia harmsiana Engl. (Moraceae). The structures of the new compounds were elucidated on the basis of 1D and 2D NMR experiments. Some isolated compounds were evaluated for their antimicrobial activities. The lupeol and its three long-chain alkanoic acid esters showed antifungal and antibacterial activities.     

Secondary metabolites from polar fractions of Piper umbellatum

Seven known secondary metabolites were isolated from the methanol extract of the branches of Piper umbellatum. The identification of these compounds was mainly achieved by 2D NMR spectroscopic techniques and FAB-MS. Among them, the known cepharadiones A and B can be considered aschemotaxonomic markers of the genus Piper.     

Antihepatotoxic and antioxidant activities of methanol extract and isolated compounds from Ficus chlamydocarpa

Free radicals, in particular radical oxygen species (ROS), play an important role in the aetiology and pathogenesis of various diseases. Current research in many countries focuses on the use of local medicinal plants as a promising source of liver protective agents. This paper describes the hepatoprotective effects of the methanol extract and four isolated compounds from Ficus chlamydocarpa on CCl4-induced liver damage, as well as the possible antioxidant mechanisms involved in this protection. The DPPH test, along with the beta-Carotene-Linoleic Acid Model System and Ferric-Reducing Antioxidant Power assays, as well as the inhibition of microsomal lipid peroxidation were used to measure radical-scavenging and antioxidant activities. Pretreatment of rats with the methanol extract of F. chlamydocarpa before CCl4 administration, significantly prevented serum increase of hepatic enzyme markers, glutamate oxaloacetate transaminase (GOT) and glutamate pyruvate transaminase (GPT), in a dose-dependent manner. The hepatoprotection was also associated with a significant enhancement in hepatic reduced glutathione (GSH) and a marked decrease of liver malondialdehyde (MDA). Among the four compounds 1-4, isolated from the methanol extract, alpha-amyrin acetate (1) and luteolin (4) showed a significant hepatoprotective activity, as indicated by their ability to prevent liver cell death and lactate dehydrogenase (LDH) leakage during CCl4 intoxication.     

Irreducibility of moduli space of harmonic 2-spheres in S4

In this paper we prove that ford3, the moduli spaces of degreed branched superminimal immersions of the 2-sphere intoS ⁴ has 2 irreducible components. Consequently, the moduli space of degreed harmonic 2-spheres inS ⁴ has 3 irreducible components.