Study on chemical composition and biological activities of essential oil and extracts from Stevia rebaudiana Bertoni leaves

Essential oil (EO), water extract (WE), and methanol-water (MWE) (50/50 v:v) were prepared from Stevia rebaudiana Bertoni leaves. Their chemicals compounds, antioxidant, anti-inflammation and antimicrobial activities were evaluated. The EO was analyzed by gas chromatography/mass spectrometry. The WE, and MWE compounds were identified by RP-HPLC. In EO, carvacrol, caryophyllene, caryophyllene oxide, spathulenol, cardinol, α-pinene, limonene, isopinocarveol and ibuprofen were identified as major compounds. Furthermore, in the WE and MWE, the major compounds were, quercetin dihydrate, protocatechuic acid and quercetin glucosyl. These results show that S. rebaudiana EO and extracts possess high antioxidant, anti-inflammation and antimicrobial properties. The antimicrobial and antifungal activities of the extracts (EO, WE, MWE) were tested on Staphylococcus aureus; Bacillus subtillis; Escherichia coli; Pseudomonas aeruginosa; Aspergillus niger and Candida albicans, the lowest activity was founded on the EO extract.     

Assessment of the microbial diversity of Brazilian kefir grains by PCR-DGGE and pyrosequencing analysis

The microbial diversity and community structure of three different kefir grains from different parts of Brazil were examined via the combination of two culture-independent methods: PCR-denaturing gradient gel electrophoresis (PCR-DGGE) and pyrosequencing. PCR-DGGE showed Lactobacillus kefiranofaciens and Lactobacillus kefiri to be the major bacterial populations in all three grains. The yeast community was dominated by Saccharomyces cerevisiae. Pyrosequencing produced a total of 14,314 partial 16S rDNA sequence reads from the three grains. Sequence analysis grouped the reads into three phyla, of which Firmicutes was dominant. Members of the genus Lactobacillus were the most abundant operational taxonomic units (OTUs) in all samples, accounting for up to 96% of the sequences. OTUs belonging to other lactic and acetic acid bacteria genera, such as Lactococcus, Leuconostoc, Streptococcus and Acetobacter, were also identified at low levels. Two of the grains showed identical DGGE profiles and a similar number of OTUs, while the third sample showed the highest diversity by both techniques. Pyrosequencing allowed the identification of bacteria that were present in small numbers and rarely associated with the microbial community of this complex ecosystem.     

Annealing Temperature Effect on Bismuth Induced Crystallization of Hydrogenated Amorphous Silicon Thin Films

Silicon - In this work, we emphasis on the Bismuth induced crystallization of hydrogenated amorphous silicon (a-Si) thin films. 50 nm of bismuth thin films are deposited by vapor...     

Adaptive observer design for uncertain nonlinear ODE-PDE cascades

We are revisiting the problem of adaptive observer design for systems that are constituted of an Ordinary Differential Equation (ODE), containing a globally Lipschitz function of the state, and a linear Partial Differential Equation (PDE) of a diffusion–reaction heat type. The ODE and PDE are connected in series and both are subject to parametric uncertainties. In addition to nonlinearity and uncertainty, the system complexity also lies in the fact that no sensor can be implemented at the junction point between the ODE and the PDE. In the absence of parameter uncertainty, nonadaptive state observers are available featuring exponential convergence. However, convergence is guaranteed only under the condition that either the Lipschitz coefficient is sufficiently small or the PDE domain length is sufficiently small. To get around this limitation, and also to account for parameter uncertainty, we develop a design that involves two concatenated adaptive observers, covering the two subintervals of the PDE domain. The proposed design employs one extra sensor, providing the measurement of the PDE state at an inner position close to the ODE-PDE junction point. Both observers are shown to be exponentially convergent, under ad-hoc persistent excitation (PE) conditions, with no limitation on the Lipschitz coefficient and domain length.     

Chemical Synthesis of Organo-siloxene 2D Materials from Calcium Di-Silicide: Characterization,Dielectric and Electrochemical Studies

Silicon - Silicon is one of the most used materials in semiconductors and electronic devices. Its miniaturization in two-dimensional (2D) scale is now a great challenge to improve and/or extend its...     

Natural convection coupled to surface radiation in an air-filled square cavity containing two heat-generating bodies

The present numerical study focuses on the cooling by natural convection and surface radiation of two electronic components generating two different and uniform volumetric powers. These components are modeled by two square bodies placed inside a closed square cavity with a cold straight wall. Two configurations are analyzed based on the position of the two heat-generating bodies. In the first one (horizontal position configuration), the two bodies are located at the same height of the cavity, while they are placed at different heights in the second case (vertical position configuration). The effects of two Rayleigh numbers ($0\le ({\mathit{Ra}}_1,{\mathit{Ra}}_2)\le {10}^6$), the conductivity ratio ($0.01\le K\le 100$), and the emissivity ($0\le \epsilon \le 1$) on the heat transfer characteristics and the flow structure are analyzed. The data is displayed as streamlines, isotherms, velocity, and maximum temperature profiles, and local heat transfer on the active wall. The obtained results indicate that the choice of the appropriate configuration depends mainly on the deviation between the two Rayleigh numbers. Furthermore, the maximum temperature of a specific block decreases as the quantity of heat generated by the other block rises. We can also see that the maximum temperature of the two blocks decreases by about $50\%$ with the increase in the emissivity (from $0$ to $1$) or the conductivity ratio (from $0.1$ to $1$).