1,720,976 research outputs found
Phytochemical investigation on leaves extractof Cordia salicifolia Cham.
No full textThe dichloromethane extract of leaves of Cordia salicifolia Cham. (Family Boraginaceae) was fractionated by SiO2 column chromatography and analyzed by gas chromatography, gas chromatography-mass spectrometry, and nuclear magnetic resonance spectroscopy. The apolar extract is characterized by a very high content of (+)-spathulenol (0.53%). The major component of the extract exhibited a very weak activity as an inhibitor of growth of Helicobacter pylori in vitro (minimum inhibitory concentration = 200 μg/mL)
Chemical Composition, Antioxidant Activities and Protective effects of Sideritis italica Extract on C2C12 Oxidative stress
No full textAims: Sideritis italica is a medicinal plant used for medical purposes mainly based on experiences rather than scientific evidence. Biological properties, composition of primary and secondary metabolites as well as the antioxidant capacity were investigated on samples from wild plant.
Methodology: The ultrastructure of aerial parts and quantitative distribution of pigments, including chlorophylls and amino acids, as well as the main class of secondary metabolites (phenols, flavonoids, flavonols and proanthocyanidins) were investigated. The extracts were tested by radical scavenging assays (DPPH, ABTS) and pharmacological assays (antiproliferative activity, effects on ROS production and protective effects against DNA damage induced by hydrogen peroxide) for their effects on C2C12 cell line.
Results: Scanning electron microphotography confirms the presence of pharmacognostic characteristics, such as glandular and non-glandular trichomes on aerial parts. The chemical analysis indicates that the leaves are the most important part of the plant, and ethanol/water 70/30 is the preferable extraction solvent. The highest concentration of all metabolites was found in 70% ethanol extract of leaves. The antiradical assays and the in vitro tests on mouse myoblast cells C2C12 confirm the biological activities of the extract. C2C12 culture medium supplemented with extract, at doses (5-200μg/ml) not interfering with cell viability, was seen to modulate the ROS production and balance the increased oxidative stress induced by hydrogen peroxide. The treatment of C2C12 cells with 200 μg/ml of extract results in a percentage reduction of ROS of -60% and -71%, compared to untreated and H2O2 treated groups, respectively, P<.05. The quantitative reduction of 8-hydroxy-2’-deoxyguanosine (8-OH-dG), which is a biomarker of free radical DNA damage, confirms the protective effect of S. italica extract on oxidative stress at basal condition as well as in presence of exogenous stimuli (-11 and -7%, at 20μg/ml, respectively versus untreated and H2O2 groups, P<.05).
Conclusion: The results obtained in the present study support the rational base for the medicinal use of plant and extracts in modulating the free radical metabolism and balancing the oxidative stress
Chemical composition, antioxidant activities and protective effects of Sideritis italica extract on C2Cl2 oxidative stress.
No full textAn unstable 0D model of ionization oscillations in Hall thruster plasmas
Full text linkThe breathing mode is an instability typical of Hall thrusters, which is characterized by oscillations of the discharge current with amplitude of the order of its mean value and frequency in the 5–30 kHz range. The strong link between this instability and the ionization processes is generally recognized. If, on one hand, 1D simulations have shown to be able to reproduce the breathing mode, on the other hand 0D models fell short in recovering self sustained oscillations, making it hard to identify the core physical mechanism governing their formation. In this work an original 0D model is presented and characterized by means of linear stability analysis and direct numerical integration. The electric field is allowed to vary in response to variations of the neutral density, acting on the ionization rate via the electron temperature and the ion dynamics. It is shown that the model is able to reproduce self-sustained oscillations with the typical characteristics of the breathing mode, even when fluctuations of the electron temperature are neglected. The stability of the model is strictly determined by the rigidity with which variations of neutral density reflect into variations of electron mobility
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
On the onset of breathing mode in Hall thrusters and the role of electron mobility fluctuations
Full text linkBreathing mode is an ionization instability which is observed ubiquitously in the operation of Hall thrusters. It is recognized as a relatively low frequency (10-30 kHz) longitudinal oscillation of the discharge current and the plasma parameters. Although breathing instability is widely studied in the literature, the conditions for its origin are not fully understood. In this work we investigate the mechanisms responsible for the origin of the breathing mode in Hall thrusters by using a numerical model, allowing us to highlight the importance of electron mobility fluctuations for the onset and self-sustenance of the instability. Our one-dimensional, fully fluid model of the thruster channel is calibrated against the measured discharge current signal for a 5 kW-class Hall thruster operating in a condition where breathing mode is fully developed. The corresponding steady, unstable configuration (base state) is numerically computed by applying the Selective Frequency Damping (SFD) method. Then, a series of numerical tests is performed to show the existence of a feedback loop involving fluctuations around the base state of the neutral density, electron mobility, and electric field. We show that oscillations of the electron mobility are mainly caused by variations of the neutral density and are in phase with them; this, in turn, induces oscillations of the electric field, which are in phase opposition. The electric field acts simultaneously on the electron temperature and on the ion dynamics, promoting the depletion and replenishment of neutrals in the chamber
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