Cryopreservation of Arachis species by vitrification of in vitro-grown shoot apices and genetic stability of recovered plants

A storage protocol at cryogenic temperature was established for shoot apices from in vitro plants of the cultivated groundnut (Arachis hypogaea) and wild Arachis species (A. retusa and A. burchellii) using a basic vitrification protocol with direct immersion in liquid nitrogen (LN). The effect of pre-treatments of donor-plants with ABA as well as of different supplements in the post-thaw culture medium was studied. After rapid warming at 40 C, the explants were cultured on MS medium devoid of growth regulators (MS0) or MS supplemented with 4.4(M benzylaminopurine (BAP) and 0.5(M naphthalene acetic acid (NAA) plus 5(M silver nitrate (AgNO3), 0.25% polyvinylpyrrolidone (PVP) or 0.2% activated charcoal. Non-frozen explants from the three species formed one shoot through meristematic amplification when cultured on MS0 medium. These explants also developed callus on MS supplemented with growth regulators (4.4(M BAP and 0.5(M NAA) alone or plus PVP or AgNO3. Callus formation was suppressed in the presence of activated charcoal. Post-thaw regeneration ocurred only through indirect organogenesis on media containing AgNO3 or PVP. Preculturing on medium supplemented with abscisic acid (ABA) improved regrowth rate in these media. Recovery failed to occur in the presence of activated charcoal. The genetic stability of shoots of A. burchellii originated from shoot apices was analyzed through Random Amplified Polymorphic DNA (RAPD) markers.     

Bifurcations and global stability of families of gradients

Dedicated to René Thom on his sixty fifth anniversary.     

On the topological classification of rarefaction curves in systems of three conservation laws

In this paper we study the topological properties of integral curves of a system of implicit differential equations associated to rarefaction curves of a system of three conservation laws. This system of equations becomes singular at the points of eigenvalue of multiplicity greater or equal to two. We focus our attention to the generic case of multiplicity two and three. We give local weak topological models for these equations.     

Diffuse X-ray scattering from several platinum chain compounds

Values of the Fermi wavevector for several platinum based one-dimensional conductors were determined from diffuse X-ray scattering measurements. The values were compared with those expected from the chemical compositions. The importance of conclusive values of this parameter is stressed and the coupling between Peierls instability and other structural instabilities is discussed.     

Production of Cyclodextrins by CGTase from Bacillus clausii Using Different Starches as Substrates

Cyclodextrins (CDs) are cyclic oligasaccharides composed by d-glucose monomers joined by α-1,4-d glicosidic linkages. The main types of CDs are α-, β- and γ-CDs consisting of cycles of six, seven, and eight glucose monomers, respectively. Their ability to form inclusion complexes is the most important characteristic, allowing their wide industrial application. The physical property of the CD-complexed compound can be altered to improve stability, volatility, solubility, or bio-availability. The cyclomaltodextrin glucanotransferase (CGTase, EC 2.4.1.19) is an enzyme capable of converting starch into CD molecules. In this work, the CGTase produced by Bacillus clausii strain E16 was used to produce CD from maltodextrin and different starches (commercial soluble starch, corn, cassava, sweet potato, and waxy corn starches) as substrates. It was observed that the substrate sources influence the kind of CD obtained and that this CGTase displays a β-CGTase action, presenting a better conversion of soluble starch at 1.0%, of which 80% was converted in CDs. The ratio of total CD produced was 0:0.89:0.11 for α/β/γ. It was also observed that root and tuber starches were more accessible to CGTase action than seed starch under the studied conditions.     

Multivariate curve resolution of pH gradient flow injection mixture analysis with correction of the Schlieren effect

Multivariate curve resolution using alternating least squares (MCR-ALS) was used to quantify ascorbic (AA) and acetylsalicylic (ASA) acids in four pharmaceutical samples using a flow injection analysis (FIA) system with pH gradient and a diode array (DAD) spectrometer as a detector. Four different pharmaceutical drugs were analyzed, giving a data array of dimensions 51 x 291 x 61, corresponding respectively to number of samples, FIA times and spectral wavelengths. MCR-ALS was applied to these large data sets using different constraints to have optimal resolution and optimal quantitative estimations of the two analytes (AA and ASA). Since both analytes give an acid-basic pair of species contributing to the UV recorded signal, at least four components sholuld be proposed to model AA and ASA in synthetic mixture samples. Moreover, one additional component was needed to resolve accurately the Schlieren effect and another additional component was also needed to model the presence of possible interferences (like caffeine) in the commercial drugs tablets, giving therefore a total number of 6 independent components needed. The best quantification relative errors were around 2% compared to the reference values obtained by HPLC and by the oxidation-reduction titrimetric method, for ASA and AA respectively. In this work, the application of MCR-ALS allowed for the first time the full resolution of the FIA diffusion profile due to the Schlieren effect as an independent signal contribution, suggesting that the proposed MCR-ALS method allows for its accurate correction in FIA-DAD systems.     

On the number of cells for flexural vibration suppression in periodic beams

Meccanica - Vibration suppression is an important topic for many engineering applications. There are different techniques, typically involving passive and active controllers. However, it can...