Centred TVD schemes for hyperbolic conservation laws

New first- and high-order centred methods for conservation lawsare presented. Convenient TVD conditions for constructing centredTVD schemes are then formulated and some useful results areproved. Two families of centred TVD schemes are constructedand extended to nonlinear systems. Some numerical results arealso presented.     

Effect of metakaolin pozzolanic activity in the early stages of cement type II paste and mortar hydration

The cement industry is one which most emits polluting gases to the environment, due to the calcium carbonate calcination, as well as to the burning of fossil fuels during the manufacturing process. Metakaolin (MK), in partial substitution to cement in its applications, is having a special worldwide growing role, for the technological increment due to its pozzolanic activity and mainly to the reduction of those emissions. In the present paper, the effect of pozzolanic activity of metakaolin was analyzed by thermal analysis in pastes and mortars of type II Portland cement in the first three days of the hydration, during which, relevant initial stages of the hydration process occur. By non-conventional differential thermal analysis (NCDTA), paste and mortar samples containing 0, 10, 20, 30 and 40% of metakaolin in cement mass substitution and using a 0.5 water/(total solids) mass ratio, were evaluated. The NCDTA curves, after normalization on cement mass basis and considering the heat capacity of each reactant, indicate that the pozzolanic activity behavior of metakaolin is different in pastes and mortars. Through the deconvolution of the normalized NCDTA curve peaks, it can be seen that ettringuite formation increases as cement substitution degree (CSD) increases, in both cases. Tobermorite formation is more enhanced in mortars than in pastes by MK, with a maximum formation at 30% of CSD. In the pastes, tobermorite formation increases as CSD increases but it is practically the same at 30 and 40% of CSD.     

Host–guest complexation of a nitroheterocyclic compound with cyclodextrins: a spectrofluorimetric and molecular modeling study

Nitroheterocyclic compounds (NC) were candidate drugs proposed for Chagas disease chemotherapy. In this study, we investigated the complexation of hydroxymethylnitrofurazone (NFOH), a potential antichagasic compound, with α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), Hydroxypropyl-β-cyclodextrin (HP-β-CD), Dimethyl-β-cyclodextrin (DM-β-CD) and γ-cyclodextrin (γ-CD) by fluorescence spectroscopy and molecular modeling studies. Hildebrand–Benesi equation was used to calculate the formation constants of NFOH with cyclodextrins based on the fluorescence differences in the CDs solution. The complexing capacity of NFOH with different CDs was compared through the results of association constant according to the following order: DM-β-CD > β-CD > α-CD > HP-β-CD > γ-CD. Molecular modeling studies give support for the experimental assignments, in favor of the formation of an inclusion complex between cyclodextrins with NFOH. This is an important study to investigate the effects of different kinds of cyclodextrins on the inclusion complex formation with NFOH and to better characterize a potential formulations to be used as therapeutic options for the oral treatment of Chagas disease.     

Anticariogenic properties of ent-pimarane diterpenes obtained by microbial transformation

In the present work, the anticariogenic activities of three pimarane-type diterpenes obtained by fungal biotransformation were investigated. Among these metabolites, ent-8(14),15-pimaradien-19-ol was the most active compound, displaying very promising MIC values (ranging from 1.5 to 4.0 μg mL(-1)) against the main microorganisms responsible for dental caries: Streptococcus salivarius, S. sobrinus, S. mutans, S. mitis, S. sanguinis, and Lactobacillus casei. Time kill assays performed with ent-8(14),15-pimaradien-19-ol against the primary causative agent S. mutans revealed that this compound only avoids growth of the inoculum in the first 12 h (bacteriostatic effect). However, its bactericidal effect is clearly noted thereafter (between 12 and 24 h). The curve profile obtained by combining ent-8(14),15-pimaradien-19-ol and chlorhexidine revealed a significant reduction in the time necessary for killing S. mutans compared with each of these two chemicals alone. However, no synergistic effect was observed using the same combination in the checkerboard assays against this microorganism. In conclusion, our results point out that ent-8(14),15-pimaradien-19-ol is an important metabolite in the search for new effective anticariogenic agents.     

High-temperature XRD study of thermally induced structural and chemical changes in iron oxide nanoparticles embedded in porous carbons

Magnetic carbon-based nanomaterials have promising applications in many fields owing to their biocompatibility and thermal/mechanical stability. This study describes a high-temperature X-ray diffraction (XRD) study of the chemical and structural transformations suffered by superparamagnetic iron oxide nanoparticles embedded in porous carbons. The nanoparticles were prepared from the decomposition of iron pentacarbonyl over porous carbons, resulting in nanometer-sized iron oxides homogeneously dispersed into the carbon matrix. The thermally induced changes in these materials were followed by in situ high-temperature XRD, using synchrotron radiation. The growing of the nanoparticles and of the carbon crystallites were first observed, followed by the reduction of the iron oxides to form α-Fe (at temperatures as low as 400 °C in some cases) and γ-Fe(C). The temperatures at which these chemical reactions occurred were dependent on the total time spent on heating and on the nature of the iron oxides formed in the as prepared materials. A noticeably large thermal expansion coefficient was also observed for the iron oxide nanocrystals. The formation of austenitic iron, stabilized by the presence of carbon, was found to be only partially reversible upon cooling.     

Host–guest system of 4-nerolidylcatechol in 2-hydroxypropyl-β-cyclodextrin: preparation, characterization and molecular modeling

The interaction of 4-nerolidylcatechol (4-NRC), a potent antioxidant agent, and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was investigated by the solubility method using Fourier transform infrared (FTIR) methods in addition to UV–Vis, ¹H-nuclear magnetic resonance (NMR) spectroscopy and molecular modeling. The inclusion complexes were prepared using grinding, kneading and freeze-drying methods. According to phase solubility studies in water a B_S-type diagram was found, displaying a stoichiometry complexation of 2:1 (drug:host) and stability constant of 6494 ± 837 M^?1. Stoichiometry was established by the UV spectrophotometer using Job’s plot method and, also confirmed by molecular modeling. Data from ¹H-NMR, and FTIR, experiments also provided formation evidence of an inclusion complex between 4-NRC and HP-β-CD. 4-NRC complexation indeed led to higher drug solubility and stability which could probably be useful to improve its biological properties and make it available to oral administration and topical formulations.     

Application of abrupt cut-off models in the analysis of the capacitance spectra of conjugated polymer devices

In this paper, a detailed study of the capacitance spectra obtained from Au/doped-polyaniline/Al structures in the frequency domain (0.05 Hz–10 MHz), and at different temperatures (150–340 K) is carried out. The capacitance spectra behavior in semiconductors can be appropriately described by using abrupt cut-off models, since they assume that the electronic gap states that can follow the ac modulation have response times varying rapidly with a certain abscissa, which is dependent on both temperature and frequency. Two models based on the abrupt cut-off concept, formerly developed to describe inorganic semiconductor devices, have been used to analyze the capacitance spectra of devices based on doped polyaniline (PANI), which is a well-known polymeric semiconductor with innumerous potential technological applications. The application of these models allowed the determination of significant parameters, such as Debye length (≈20 nm), position of bulk Fermi level (≈320 meV) and associated density of states (≈2×10¹⁸ eV⁻¹ cm⁻³), width of the space charge region (≈70 nm), built-in potential (≈780 meV), and the gap states’ distribution.     

A note on gradient k-Yamabe solitons

Annals of Global Analysis and Geometry - In this paper we provide some triviality results for gradient k-Yamabe solitons under different assumptions. In fact, under either growth or integral...