Online distance mathematics education in Brazil: research, practice and policy

In this article, we address online distance mathematics education research and practice in Brazil, which are relative newcomers to the educational scene. We present the national context of education in Brazil, highlighting the organization of the educational system, and also a summary of national legislation on distance education and an overview of digital inclusion in the country. We outline the potential and relevance of distance education for the Brazilian educational system and show how it could intervene in the system. With respect to research and practice in online mathematics education, we present support for research, examples of studies and highlight different aspects being addressed, including its essential components. In addition, we discuss the synergy between distance education and teacher education, and mathematics distance education and modeling, as well as other initiatives in the national scenario.     

Influence of disorder on superconductivity in non-magnetic rare-earth nickel borocarbides

The effect of substitutional disorder on the superconducting properties of YNi₂B₂C was studied by partially replacing yttrium and nickel by Lu and Pt, respectively. For the two series of (Y, Lu)Ni₂B₂C and Y(Ni, Pt)₂B₂C compounds, the upper critical field H _c2(T) and the specific heat c _p(T, H) in the superconducting mixed state have been investigated. Disorder is found to reduce several relevant quantities such as T _c, the upper critical field H _c2(0) at T=0 and a characteristic positive curvature of H _c2(T) observed for these compounds near T _c. The H _c2(T) data point to the clean limit for (Y, Lu) substitutions and to a transition to the quasi-dirty limit for (Ni, Pt) substitutions. The electronic specific heat contribution γ(H) exhibits significant deviations from the usual linear γ(H) law. These deviations reduce with growing substitutional disorder but remain even in the quasidirty limit which is reached in the Y(Ni_1−x , Pt _x )₂B₂C samples for x=0.1.     

Thermodynamic and structural characterization of zwitterionic micelles of the membrane protein solubilizing amidosulfobetaine surfactants ASB-14 and ASB-16

Surface tension and isothermal titration calorimetry (ITC) were used to determine the critical micelle concentration (cmc) of the zwitterionic amidosulfobetaine surfactants ASB-14 and ASB-16 (linear-alkylamidopropyldimethylammoniopropanosulfonates) at 25 °C. The cmc and the heat of micellization were determined from 15 to 75 °C by ITC for both surfactants. The increase in temperature caused significant changes in the enthalpy and in the entropy of micellization, with small changes in the standard Gibbs energy (ΔG(mic)), which is consistent to an enthalpy?entropy compensation with a compensatory temperature of 311 K (ASB-14) and 314 K (ASB-16). In the studied temperature range, the heat capacity of micellization (ΔC(p)(mic)) was essentially constant. The experimental ΔC(p)(mic) was lower than that expected if only hydrophobic interactions were considered, suggesting that polar interactions at the head groups are of significant importance in the thermodynamics of micelle formation by these surfactants. Indeed, a NMR NOESY spectrum showed NOEs that are improbable to occur within the same monomer, resulting from interactions at the polar head groups involving more than one monomer. The ITC and NMR results indicate a tilt in the polar headgroup favoring the polar interactions. We have also observed COSY correlations typical of dipolar interactions that could be recovered with the partial alignment of the molecule in solution, which results in an anisotropic tumbling. The anisotropy suggested an ellipsoidal shape of the micelles, which results in a positive magnetic susceptibility, and ultimately in orientation induced by the magnetic field. Such an ellipsoidal shape was confirmed from results obtained by SAXS experiments that revealed aggregation numbers of 108 and 168 for ASB-14 and ASB-16 micelles, respectively. This study characterizes an interesting micelle system that can be used in the study of membrane proteins by solution NMR spectroscopy.     

Nanovesicle encapsulation of antimicrobial peptide P34: physicochemical characterization and mode of action on <Emphasis Type="Italic">Listeria monocytogenes</Emphasis>

Antimicrobial peptide P34, a substance showing antibacterial activity against pathogenic and food spoilage bacteria, was encapsulated in liposomes prepared from partially purified soybean phosphatidylcholine, and their physicochemical characteristics were evaluated. The antimicrobial activity was estimated by agar diffusion assay using Listeria monocytogenes ATCC 7644 as indicator strain. A concentration of 3,200 AU/mL of P34 was encapsulated in nanovesicles and stocked at 4 °C. No significant difference (p > 0.05) in the biological activity of free and encapsulated P34 was observed through 24 days. Size and PDI of liposomes, investigated by light scattering analysis, were on average 150 nm and 0.22 respectively. Zeta potential was −27.42 mV. There was no significant change (p > 0.05) in the physicochemical properties of liposomes during the time of evaluation. The liposomes presented closed spherical morphology as visualized by transmission electron microscopy (TEM). The mode of action of liposome-encapsulated P34 under L. monocytogenes cells was investigated by TEM. Liposomes appeared to adhere but not fuse with the bacterial cell wall, suggesting that the antimicrobial is released from nanovesicles to act against the microorganism. The effect of free and encapsulated P34 was tested against L. monocytogenes, showing that free bacteriocin inhibited the pathogen more quickly than the encapsulated P34. Liposomes prepared with low-cost lipid showed high encapsulation efficiency for a new antimicrobial peptide and were stable during storage. The mode of action against the pathogen L. monocytogenes was characterized.     

Development and validation of an HPLC-PDA method for the determination of myrsinoic acid B in the extracts of Rapanea ferruginea Mez

New, simple, rapid and precise HPLC-PDA method has been developed and validated for quantification of biomarker myrsinoic acid B in stem bark extracts of Rapanea ferruginea Mez. The method employs a Phenomenex C18 column (250 mm × 4.6 mm I.D., 5 μm) with acetonitrile:methanol:water (pH 2.6 with phosphoric acid) at 48:30:22 as mobile phase, at a flow rate of 0.7 mL min⁻¹ and photo diode array (PDA) detection at 270 nm. The validation data show that the method is specific, accurate, precise and robust. The method was linear, over a range of 5-100.0 μg mL⁻¹, with a limit of detection of 0.369 μg mL⁻¹ and limit of quantification of 1.233 μg mL⁻¹. The method has also shown consistent recoveries (average of 101.3% and 0.12% RSD) of the biomarker, with low intra and inter-day relative standard deviation (1.26% and 1.62%, respectively). The evaluated hydroethanolic extract and dry extract presented MAB values of 63.53 and 36.07 mg g⁻¹, respectively.     

Non-resonant microwave absorption studies of superconducting MgB2 and MgB2 + MgO

Non-resonant microwave absorption (NRMA) studies of superconducting MgB₂ and a sample containing ∼10% by weight of MgO in MgB₂ are reported. The NRMA results indicate near absence of intergranular weak links in the pure MgB₂ sample. A linear temperature dependence of the lower critical field H _c1 is observed indicating a non-s wave superconductivity. However, the phase reversal of the NRMA signal which could suggest d wave symmetry is also not observed. In the MgB₂ + MgO sample, much larger low field dependent absorption is observed indicating the presence of intergranular weak links. The hysteretic behavior of NRMA is compared and contrasted in the two samples. In the pure MgB₂ sample, a large hysteresis is observed between the forward and the reverse scans of the magnetic field indicating strong pinning of flux lines. This hysteresis saturates a few degrees below T _c while in the MgB₂ + MgO sample, a much slower increase of hysteresis with decreasing temperature is observed, a signature of weaker pinning.     

A new triterpene with antinociceptive activity from Maytenus robusta

A new triterpene 3,15-dioxo-21alpha-hydroxy friedelane has been isolated from methanol extract of Maytenus robusta and its structure elucidated on the basis of spectral analysis. Stigmasterol, friedelin, friedelanol and 3,15-dioxo friedelane were also obtained. 3,15-dioxo-21alpha-hydroxy friedelane was analyzed against the writhing test in mice and exhibited potent dose-dependent effects with an ID50 value of 12.5 +/- 2.1 micromol kg(-1) and a maximal inhibition of 85.90%. It was about 10-fold more active than aspirin and paracetamol, used as reference drugs.     

Characterization of Sesquiterpene Polygodial-Beta Cyclodextrin Inclusion Complex

Polygodial is a sesquiterpene drimane isolated from the genus Drimys, whichexhibits anti-asthmatic, anti-allergic, anti-inflammatory and antinociceptive effects.We have prepared a polygodial--cyclodextrin inclusion complex for furtherpharmacological studies. The inclusion complex was synthesized by co-precipitationand analyzed by Thermogravimetric Analysis, showing a decrease in the number ofwater molecules of hydration in relation to the native -cyclodextrin. DifferentialThermogravimetric Analysis indicated a peak corresponding to the evaporation ofpolygodial. With Differential Scanning Calorimetry, the melting peak to polygodial was not observed, however, there was an increase in the energy of vaporization of the water molecules in relation to native -cyclodextrin. Using a Scanning Electron Microscopy a clear difference in the morphology of crystals of the inclusion complex and native -cyclodextrin could be seen. The association constant between polygodial and -cyclodextrin, measured by UV spectroscopy was 1,006 M^-1 at 37 °C, pH 7.0 and ionic strength 0.2 M, following stoichiometry 1:1.